Polyethylene films and wax coatings, which are generally laminated or coated to paper, are widely used in packaging applications to protect products from moisture and provide water or grease resistance. However, recycling of packaging containing polyethylene films and wax coatings are limited and costly since special equipment is necessary for repulping. In addition, the polyethylene films and most wax coatings Will not degrade if the package is composted. Thus it would be desirable to find an alternative for conventional polyethylene films that has comparable moisture barrier properties but also has the added benefit of repulpability and compostability.
The present invention provides a two-step coating process wherein a substrate is coated on at least one surface with a primer and a top coat, both of which are water-based dispersions, to produce a product with moisture barrier properties and easy repulpability. The primer coat, preferably ethylene vinyl acetate, functions to seal the porous substrate to permit effective coating of the top film coat. The top coat or barrier film is preferably a combination of an aqueous acrylic copolymer, preferably a styrenated acrylic copolymer, and a wax dispersion. However, other aqueous polymer dispersions such as polyvinylidene chloride or compositions with or without a wax component can be used.
U.S. Pat. No. 3,196,038 to Schoch et al. discloses a process and apparatus for continuous application of multiple coatings (at least three) on a paper substrate to render the paper web moisture and grease resistant. The base coating is a dispersion selected from the group consisting of polyvinyl chloride,. polyvinyl acetate, polyvinylidene chloride, esters of polyacrylic acid, polystyrol, polyethylene, paraffin and mixtures thereof. The second coat, preferably of the same Composition as the base coating, provides a flexible intermediate layer to which a harder top coat is then applied.
U.S. Pat. No. 3,873,345 to Vreeland discloses a process for producing a high gloss paper with a heat calendaring apparatus. The coating composition used is comprised of a mineral pigment, such as clay and a binder selected from the group consisting of vinyl acetate, Styrene-isoprene and acrylic polymer latices. The polymer latex has a glass transition greater than 100.degree. F.
U.S. Pat. No. 4,248,939 to Parsons discloses a process for coating paper to obtain improved appearance and printablity. A paper substrate is treated with a first layer comprised of an inorganic pigment, such as clay, and binder and a second layer comprised of an organic pigment and binder. The organic pigments used in the second topcoat are prepared by graft copolymerizing in aqueous medium a monoethylenically unsaturated monomer onto a water soluble prepolymer. The water soluble prepolymers used include copolymers of vinyl alcohol and acrylic acid. The organic pigment coating compositions are used to create high gloss paper under less severe calendaring conditions than coating systems using inorganic pigments alone.
U.S. Pat. Nos. 4,265,969 and 4,301,210 to Yasuda et al. disclose processes for preparing cast coated paper having high gloss. The undercoating contains pigment binders and the aqueous overcoating consists of pigments with polymer latex binders having glass transition temperatures over 38.degree. C.
U.S. Pat. No. 4,844,952 to Korenkiewicz et al. relates to multicoated substrates having good stain and grease resistance. A conventional decorative finish coating composition, which is solvent based or aqueous, is applied to the substrate followed by application of a coating of a waterborne polymer composition free of external crosslinking agents (lacquer type coating).
U.S. Pat. No. 5,169,715 to Maubert et al. discloses a high gloss paper produced by applying two coats. The first base coat comprises a synthetic latex, starch, polyvinyl alcohol and proteins. The second gloss coating contains conventional pigments and binders. Acrylic styrene copolymers are used as gloss pigments.
From the prior art mentioned it is seen that waterborne polymers have been used in the production of high gloss paper. Additional aqueous composition coatings including acrylic latexes are shown but also include polyethylene as a component. The art does not provide a process for treating paper substrates with water based dispersions to form a packaging stock that acts as a barrier to moisture vapor and grease without using conventional polyethylene coatings. The invention is directed to the provision of Such recyclable and compostable coated paper stocks. It would be appreciated that advantage over known applications would be obtained by providing water based dispersion coatings which are more readily recycled than polyethylene films and wax coatings and in the provision of a two-step coating process to produce a product with moisture barrier properties and easy repulpability. The water-based coatings of the invention provide an alternative for conventional polyethylene coatings. This obtains an advantage over the prior art since the coated paper can easily be repulped without special flotation equipment, which is needed when repulping polyethylene film. The water-based coatings disperse in water, allowing the paper fibers to be easily reclaimed for reuse. The coated paper of the invention also readily disintegrates when composted.
Accordingly, it is a broad object of the invention to provide a recyclable and compostable coated paper stock comprised of a substrate coated with a primer coat and a top coat, both of which are water-based dispersions.
A more specific object of the invention is to provide a recyclable and compostable coated paper stock having water resistance, grease resistance and moisture vapor barrier characteristics.
Another object of the invention is to provide a recyclable and compostable coated paper stock which is formed into a package or container.
A specific object of the invention is to provide a recyclable and compostable coated paper stock that is readily compostable/biodegradable.
A more specific object of the invention is to provide a recyclable and compostable coated paper stock that is readily recycled without dependence on special equipment for repulping.